Recently, nanotechnology has been applied in various fields, including physics, chemistry, materials science, biology, and medicine. Nanotechnology is also applied in the removal of multiple impurities/pollutants, including pathogenic bacteria and viruses, from water and other water bodies. Among the various methods used for wastewater treatment, adsorption is one of the more effective methods due to its low cost and simplicity of operation. Moreover, many methods of NP synthesis are expensive and not environmentally sustainable. The utilization of biomass as a source for the production of NPs has the potential to mitigate issues pertaining to cost, sustainability, and pollution. The utilization of bio-based nanomaterials (bio-NMs) sourced from biomass has garnered attention in the field of water purification due to their cost-effectiveness, biocompatibility, and biodegradability. Several research studies have been conducted to efficiently produce NPs (both inorganic and organic) from biomass for applications in wastewater treatment. Recently, nanoadsorbents have been explored for removing various pollutants from wastewater. In this chapter, the utilization of NMs as an effective adsorbent for removing heavy metals, organic compounds, pesticides, pharmaceuticals, and microplastic pollutants is reviewed and discussed. It is to be mentioned that the adsorption capacities of the adsorbents vary depending on the characteristics of the adsorbents, the extent of chemical modification, and the concentration of adsorbates. There are also a few issues and drawbacks in the utilization of nanoadsorbents that have been addressed. To determine the practical application of NMs as low-cost adsorbents on a commercial scale, further research in this direction is needed. This chapter demonstrates that NMs can be effectively utilized for wastewater treatment and may be novel and promising adsorbents/materials for future water treatment applications.